1. Field of the Invention
The present invention relates to a method and a device for operating a hybrid drive device having an internal combustion engine, another drive unit, and a separating clutch which is engaged to start the internal combustion engine.
2. Description of Related Art
Such methods and devices are already known from the related art. Hybrid vehicles having a parallel hybrid drive usually have an internal combustion engine, at least another drive unit, in particular an electric machine, and a transmission for setting the transmission ratio between input and output in the drivetrain. If there is a separating clutch between the internal combustion engine and the other drive unit, then the vehicle may be driven jointly by the internal combustion engine and the other unit, or by only the other unit alone. If the vehicle is driven only by the other unit, then the internal combustion engine may be started by engaging the separating clutch. As long as the internal combustion engine is not yet generating any drive torque, it counteracts the torque of the other drive unit. As soon as the internal combustion engine is started, the drive torque of the internal combustion engine is added to the drive torque of the other drive unit. The start of the internal combustion engine is a dynamic process, which exhibits an irregular pattern of the drive torque of the internal combustion engine. To ensure comfortable driving of the vehicle, the drive torque of the drivetrain should not be disturbed by this dynamic start. Instead, the drive torque of the drivetrain should always correspond to the driver's torque request.
A method for operating a hybrid drive device is known from published international patent application document WO 2008/043712 A1. To start the internal combustion engine, a separating clutch is engaged. It is provided that, as a function of the rotational speed of the turbine wheel of the torque converter, such a rotational speed is predefined for the electric machine that no torque jump occurs at the hybrid drive during the starting process of the internal combustion engine.